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' H. BLAGKMAN. PROCESS OF AND APPARATUS FOR DISINTEGRATING FIBERS AND MANUFACTURING PAPER PULP.

No. 369,834. Patented Sept. 13, 1887.

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2 ..b e e h S P t e e h S 3 N A M K C A L B H m a 0 M O R DISINTEGEATING FIBERS AND PROGBSS OF AND APPARATUS F0 MANUFAGTURIN G PAPER PULP.

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' MANUFACTURING Patented Se t. 13, 1887.

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HENRY BLAGKMAN, OF NEW YORK, N. Y.

PROCESS OF AND APPARATUS FOR DISINTEGRATING FIBERS AND MANUFACTURING PAPER-PULP.

$PECIPICATION forming part of Letters Patent NO. 369,834, dated September 13, 1887,

Application filed August 30, 1886. Serial No. 212,147. (No model.)

To ctZZ whom it may concern..- 1

Be it known that 1', HENRY BLAOKMAN, a citizen of the United States, residing in the city, county and State of New York, have invented eertain new and useful Improvements in Processes of and Apparatus for Disintegratng Fibers and Manufacturing Paper-Pill p, of

which the following is a specification.

This invention relates to the disintegration of fibers from straw, wood, and other fiberbearing materials for the manufacture of paper-pulp.

In my application forpatent for improvements in disintegrating fibers and manufacturing paper-pulp, filed May17, 1886, I have described a new method of disintegrating fibrous substances by first softening them by treatment in a digester and then blowing them out under heavy pressure and at a high temperature into a vacuumchamber, wherein a par tial vacuum is maintained in order to cause a sudden or explosive disruption of the softened fibrous substances.

My present invention relates most particularly to the treatment of the fibrous matter in the digester and also partly to the subsequent treatment of the disintegrated fibers. My invention includes,also, certain improvementsin the apparatus especially designed to facilitate the practice of this process.

According to my present invention, I first introduce the fibrous matter into a digester in a coinminuted condition. If wood is used, it is in the form ofsmall chips or granules. The digester is closed and water is turned on with or without chemicals, steam is injected, and the mass is boiled under pressure until the fibrous matter becomes softened. The liquor is pumped out and returned to the digester, thereby causing a circulation through the mass. A vacuum-valve in a pipe leading to a suction-pump is then opened slightly to cause a circulation or outflow of any vapors, chemicals, or impurities that may be at the top of the mass, but without losing the pressure. Gases or chemicals may be forced through the mass while the boiling continues. The

' liquor is drawn off and any chemicals that may have been used are recovered. Steam is then injected into the mass, the vacuum-valve is fully opened, and the mass is boiled in vacuo for a sufficient length of time, whereby all vaporizable impurities are carried ofif. Then the valve is closed, the fibrous matter is drained of its liquor, and clean hot water is introduced, and the mass is again boiled under pressure with forced circulation, and finally in cacao again. Finally pressure is turned on, the outlet-valve is opened, and the fibrous mass and water are forced out of the digester in a slow stream and enter through a contracted nozzle into a vacuum-chamber, in which the sudden expansion of the steam in the fibers disruptsthem explosively, the fibers being forcibly torn apart. In this chamber the vacuum is maintained by showering cold water to condense the steam and by the suction of a pump. The fibers and water are carried from the vacuum-chamber through a grit-separator containing a succession of traps for catching the sand and heavier particles and pass thence through a force-p11 mp, by which they are caused to flow through an agitator, wherein the fibrous matter is reduced to a condition of homogeneous fiocculence.

Figure 1 of the accompanying drawings is a side elevation of the apparatus used by me for the manufacture of paper-pulp according to my present invention. Fig. 2 is a plan thereof. Fig. 3 is a vertical section of the portion of the apparatus to which'my present invention pertains. Fig. 4 is a horizontal section of the digester on the line 4 4. in Fig. 3. Fig. 5 is a vertical transverse section of the vacuumchamber and grit-separator. Fig. 6-is an elevation of a modification, partly in vertical sec tion; and Fig. 7 is a sectional elevation of another modification.

I will now proceed to describe the apparatus, referring first to Figs. 1 and 2. A is the digester. B is the vacuumchamber. 0 is the grit-separator. D and E are pumps. F is an agitator, and G is a scrubber, which is in the same casing as the agitator. These machines are connected together through suitable pipes, so as to operate in succession.

Figs. 3 and 4. show the digester A in detail.

It consists, preferably, of an upright cylinder of wrought iron or steel, with rounded bottom and lined or coated internally with some substance which will resist the corrosive action of the chemicals used for treating the fibrous matter. At the top of the digester is a man-hole, a, through which to introduce the fibrous matter to be treated. At the bottom of the digester is an outlet-valve, L, from which a pipe, L, leads to the vacuum-chamber B, which it enters, its end being contracted to form a nozzle, 1). Within the digester are four (more or less) perforated vertical pipes M M. These are connected at the top to horizontal pipes N N, and at the bottom tohorizontal pipes N N. These pipes N and Nare in the form of rectangles. A steam-pipe, S, leads from a steam-boiler (not shown) and enters the top of the digester, having a branch, S which joins the pipes N. A steam-pipe, S, joins the pipes N, and has a branch, S", which enters the valve L. This valve is a three-way valve, being adapted to connect the outlet of the digester with either the outletpipe L or the steam-pipe S. A water-pipe, W, is connected with the pipes N. A pipe, 0, leads from a tank, A, Fig. 1, for containing chemicals and connects with the pipes N, and another pipe, 0, leads from this tank (or another chemical-tank) and joins the pipes N.

In the bottom of the digester is a conical perforated screen or grating, a 0, inclined toward the outlet L, and from beneath this grating a drainage-pipe, 0', leads downward to the pipes N. From the pipes N a pipe leads to a pump, P, which is shown as a rotary or centrifugal pump, (although any kind of pump may be used,) and from this pump extends a delivery-pipe, P, which leads upward and connects with the pipes N at the top. By means of this pump a liquid can be drawn off from the bottom of the digester and forced in at the top, thus establishing a circulation. A heater or jacket, P is arranged to heat (or cool, as the case may be) the liquid passing through the pipe 1?.

From the top of the digester a suction-pipe, E, leads to the vacuum-chamber B, and from this chamber another suction-pipe, E, leads to the pump E, from which a discharge-pipe, E extends to a condenser or a tank or other 7 device, (not shown,) whereby the chemicals drawn off by the pump may be recovered. A branch pipe, N connects the pipes N and I with the suction-pipe E.

The several pipes above referred to are provided with Valves or cocks to control the flow of the liquid through them. These valves are numbered, and will be referred to by their numbers in describing the process.

The vacuum-chamber B is partially divided by a vertical partition or target, at, into two chambers, B and B", as shown in Fig. 3. In the chamber 13 are two perforated waterpipes, e 6, Fig. 5, designed to shower water into this chamber on opposite sides of the nozzle b. In the chamber B there is one perforated water-pipe, e, which showers water into this chamber. From the upper part of this chamber the suction-pipe E leads to the pump E, which maintains the vacuum, its entrance being guarded by a shield, 6 In this pipe is a perforated pipe, 0, which is adapted to shower water into the pipe E, to condense any steam or vapor therein.

From the bottom of the chamber B the outlet-pipe b leads down into the grit-separator C. This is a closed box in which is constructed a double series of traps or pockets for catching grit, sand, and other heavy particles in the pulp-such as bits of knots which have not been disintegrated. Beneath the inlet 1) are two converging partitions, b b and on each side of these is a dam, 0, over which the liquid must flow, then a partition, 61, under which the liquid must flow, then another dam lower than the first, then another partition, and so on. As the liquid runs over the last dam on each side it falls on an inclined plate, f, Fig. 3, which carries it toward the front, and it then runs back under the false bottom f of the traps and out the pipe D to the pump D. The delivery-pipe D from this pump leads to the agitator F, Fig. 1. This agitator and the scrubber G, and other apparatus used for finishing the pulp, are fully described in another application executed by me this day.

I will proceed to describe the operation in detail. The comminuted fibrous matter is put into the digester through the man hole a, which is then closed. If it is to be boiled first with water alone, this is admitted through the pipe WV by opening valves Nos. 1, 4, 5, and 6, whereby the water is caused to ascend through the pipes M M and to flow out from theirperforations into the fibrous mass. If the mass is to be treated with chemicals, they are drawn from a tank or vat through pipe 0 by opening valves 12, 13, 14, and 15, or through pipe 0 by opening valves 3, 4, 6, and 5, so that in either case the chemical enters through the pipes M M. When the Inassis saturated, the wateror chemical is turned off and steam is turned on by opening valves 1 and 9, or by valves 1, 4, 5, and 6, or by valve 11, and the material is boiled under pressure for about half an hour, (more or less.) After sufficient steam has been introduced it is shut off and a forced circulation is instituted by means of the pump 1?. There are several ways of doing this. By closing valves 4 and 5 and opening valves 8, 7, 16,14, and 15 the liquid will be drained off through the screen 0, and returned at the top through the pipes M M, causing a circulation downward; 'or'the liquid may be drawn off through any one of the pipes MMand returned through another or the'other pipes by, for instance, closing valves 4 and 15, and opening valves 5, 7, 16, and 14, in which case the current will flow through the mass from left to right between the pipes. Steam may be injected at the same time either through pipe S and valve 11, or through pipes S, N, and M, by opening valves 1 and 4, or 1, 6, and 5, or 1, 6, and 8, or 1 and 9. The valve 9 should be opened at intervals during the entire operation in order to inject steam through the outlet and effect the disintegration of the material in and near the outlet. After a time the vacuumvalve 18 is opened very slightly, sufficiently to draw off any gases, impure vapors, or light gummy 0r resinous matters that may have risen to the top of the mass during the boiling. A vacuum is maintained by running the pump E. The pressure in the digester is kept up and the material is kept boiling by entering steam at the bottom. The steam thus oirc'ulates upward through the mass, thereby carrying off the vaporizable impurities, which pass out through the vacuum-valve. valve is opened so slightly that the outflowing vapors are choked and the pressure in the digester is maintained sufficiently high to force the steam into all the interstices of the fibrous mass, whereby a very thorough disintegration is effected at the same time that all the advantages of a circulation of steam and the carrying off of the vaporizable impurities are attained. Vhile the boiling continues any gases or chemicals for disintegration or bleaching may be forced through the mass. Gases, such as sulphurous acid, will be entered at the bottom and be drawn off at the top by the vacuun pipe E. To recover them they will be cooled and passed through water, which will absorb them. This may be done by showering water from the perforated pipe 0" and by carrying the pipe E" to a worm or condenser. After a sufficient boiling the liquor is drained off from the mass. This may be done by opening valves 4, 5, 6, and 3 and by turning in steam on top of the mass, blowing out the liquid through the pipe 0; or by opening valves 8, 7, and 17 the liquid may be drawn off by the pumps P and E, after which the chemicals are regenerated to be used again. Vhen all the liquor is drained off, steam is turned into the bottom of the digester, the vacuunrvalve 18 is fully opened, and the mass is boiled in vacuo for, usually, from one to two hours, the steam rising through the mass vaporizing such impurities as are vaporizable, and passing off with them through the pipes E E to the pump E. During this boiling in. cacao any desired chemical may be introduced into the digesterfieither a liquid or gas. After a sufficient, time the valve 18 is closed and the fibrous matter is drained of its liquor or chemical, as before, and then clean hot water is introduced through -the valves 2, 4, 6, and 5 until the mass is thoroughly saturated. The fibrous mass is also to be rinsed once or more during the treatment in the digester, and I prefer to drain off the old liquor and supply clean water simultaneously with the rinsing process. This is done by opening the vacuum-valve 18, while running the pump E, and introducing the clean water at the bottom. The fibers, being thoroughly soaked by the previous boiling, are heavy and do not float in the liquid, but lie while the liquid slowly rises through them.' The foul liquor is lifted by the water beneath it and flows out through the pipe E, being discharged from pump E into a suitable receptacle. This process is continued until the liquid coming off in this way runs clear, show- This ing that all unattached dirt in the fibrous mass has been carried out. This rinsing is best practiced with an upward current, as it opens out the fibers and the water penetrates to all parts, whereas a downward current would tend to pack the fibers together at the bottom. \Vhen the rinsing is completed, steam is turned on at full pressure, and the mass is boiled for a short time, the liquor being circulated by the pump P, as before described. Then the valve 18 is opened and the vapors are carried off again, and the mass is again boiled in cacao for a few minutes.

In practicing this process any ordinary steam-p ressu re may be usedsay, for instance, from ten to one hundred pounds. The vacuum should be about twenty-seven inches, although this may vary considerably. The pressures, temperatures, and duration of the different steps must be modified according to the character of the material under treatment.

When the digesting process is completed, the vacuum-valve is closed, steam is turned on at valve 11, and the pressure is run up to the maximum. Then the outlet-valve L is opened and the mixed fibrous matter and water is blown out through the pipe L and nozzle 12 into the vacuum-chamber B, in which a vacuum of about twentyseven inches is maintained by the pump E. Both pumps D and E are kept running during the discharging of the digester. The contracted nozzle chokes back the steam; but as it passes the nozzle it is suddenly released into the vacuum and the steam and superheated water in the interstices of the fibers expand with great force, tearing the fibers apart with an explosive action. Immediately the steam thus liberated is cooled and condensed by water showering from the pipes e and 6. thus admitted unites with the fibers and washes them through the condensing-chamber and down the outlet 6 into the grit-separator G. In passing through the traps in this separator the grit and other heavy particles are thrown to the bottoms of the traps, the fibrous matter or pulp being thus freed from particles of grit before it passes to the pump 1), so that the pump is protected from injury by the grit. This pump D acts to draw off the liquidfrom the vacuum-chamber, draw it through the traps in the grit-separator,and force it through the agitator F and scrubber G. In the agitator the pulp is forced through tortuous passages and around obstructions, whereby any fibers that may be clinging together are gently separated, and in the scrubber the fibers are rubbed between opposite bristle brushes, whereby their separation is completed. The pulp when it emerges from the separator is homogeneous, its fibers being reduced to a fioeculent condition.

The grit-separator G is provided with a pipe, f, by which to drain it of liquid. Ordinarily a quantity of liquid is retained in this chain her by the pipe D rising into it aboveits bottom. This enables any heavy particles not The water IIO Wall.

caught by the traps to be precipitated on the bottom. The separator may be opened for cleaning by taking off an end plate, f which exposes the bottoms of all the traps.

Prior to my invention difficulty has been experienced in effecting a thorough disintegration of the material in and near the outletof the digester, the result being that the portion of the material lying in and near the outletpassage has at the termination of the digesting process been very slightly acted upon. As this is the portion which is first expelled in blowing off the digester, it is liable, when thus undigested, to clog the outlet or the nozzle 1) and occasion serious difficulty; hence it is very important that it shall be digested as thoroughly as the remainder of the material. This I accomplish by making the valve L a twoway cock and by supplying the branch pipe S" and its valve 9. The valve L is kept turned toward the pipe S during the digesting operation, so that steam, water, or chemicals may at intervals be injected through the pipe S to act upon this portion of the material.

The digester A is constructed with double walls, forming a surrounding jacket, 9. The inner Wall is lined with (or made of) lead or other material that will resist the action of the chemicals. The outer wall is of great strength, sufficient to resist the internal pressure in the digester. From the upper part of the jacket a pipe, 9, leads to a chamber, a, which is fitted with a water'gage. From this chamber a pipe, extends downward to a pump, at, thence through a heater, a, and finally enters the lower part of the jacket 9. WVater is admitted to thejacket and pipes through a pipe, 9, and the water is kept in circulation by the pump a. If any leakage occurs through the inner walls, the matter which passes through is immediately diluted by the water in the jacket, and is prevented from attacking the metal of the outer wall. The water is drawn off from time to time, so that it never becomes so impregnated with leakage as to corrode the outer A test-paper may be used to determine if any leakage has occurred.- The heater (0 serves to keep the temperature of the waterjacket up to that within the digester. The pressure is balanced on both sides of the inner wall by meansof a pipe, 9', which taps the pipe S to the right of the valve 11, thereby communicating with the interior of the digester. If any fumes accumulate in the chamber a, they may be drawn offthrough a vacuum-tube, f, which leads to the pipe E.

My invention may be operated with any practicable chemical process of d sintegration, such modification of one or the other being made as is necessary to adapt them to each other. It is especially desirable with the sulmethod of applying this agent. cess the fibers are not exposed to the air at any stage of the treatment, whereby oxidation or discoloration is prevented, the impurities being all washed out or bleached out before exposure to the air. The result is that the pulp made by my process is very nearly white, even without bleaching. By the alternate boiling under pressure and boiling in vacuum the vaporizable impurities are vaporized and carried off, and the fibers are purified to an extent not before possible, so far as I am aware.

My invention enables paper-pulp to be made from horse-manure, bedding-straw used in stables, and other impure substances the use of unprofitable.

My invention is subject to considerable modification, both in the process and apparatus. The precise manipulations will be varied to adapt the treatment to different materials.

With some materials the complete separation of the fibers can be effected in the digester, and in such case the operation of blowing or exploding into a vacuum-chamber may be omitted;

Fig. 6 shows an apparatus in which the vacuum-chamber is omitted, and in which one pump, D E, takes the place of the two pumps D and E, being adapted to draw from the pipe E during the digesting and from the pipe D during the discharge. The digester is discharged directly into the grit-separator G, sufficient water being added to the fiber, either in the digester or separator, to carry it through the traps and enable it to be pumped.

In practicing my invention there will usually be several digesters, in order that the process in the remaining apparatus may be made practically continuous. WVh'en only one digester is used, the remainder of the apparatus must remain'idle the greater portion of the time while the digesting is being done, but with several digesters they can be operated in succession, so that when one is blown off another will be ready or nearly ready to be blown off, thus economizing time to theutmost, and keeping the remaining apparatus constantly at work.

Fig. 7 shows a modified arrangement of apparatus which may be preferred for some purposes. The digesters A A are arranged in a row, and beneath them extends a prolonged vacuum-chamber, B, connected by a pipe, 'E, to the pump E. Beneath the vacuum-chamber is the grit-separator G, which connects by pipe D to pump D.

Many other constructions and arrangements may be adopted without departing from the essentials of my invention.

What I claim,and desire to secure by Letters Patent. is-

,1. The improvement in the art of disintegrating fibrous substances, which consists in boiling them in a suitable vessel under pressure by injecting steam at the bottom of the vessel, causing it to pass through the mass of material, and escaping the resulting vapors from the upper part of the vessel through a which has heretofore been impracticable or I contracted opening, whereby a circulation through the mass is maintained under pressure and at a high temperature and the vapor izable impurities are dissolved, vaporized,and expelled.

2. The improvement in the art of disintegrating fibrous substances, which consists in boiling them under pressure in a closed vessel and subsequently introducing steam at the bottom of the vessel, causing it to pass through the mass of material, and escaping the resulting vapors from the top, whereby the impurities are first dissolved at a high temperature and are then vaporized and expelled.

3. The improvement in the art of disintegrating fibrous substances, which consists in boiling them in a digester under pressure and subsequently boiling them under a partial vacuum and drawing off from the digester the vapors arising therein, whereby the impurities are first dissolved and then vaporized and carried off.

4. The improvement in the art of disintegrating fibrous substances, which consists in boiling them in a digester under pressure, drawing off the vapors arising in the digester while introducing steam to maintain the press-' ure, and subsequently boiling in vacuum.

5. The improvement in the art of disintegrating fibrous substances, which consists in boiling them in a digester under pressure, drawing off theliquor and returning it to the digester, wherebyaforced circulation through the mass is maintained, then draining off the liquor, injecting steam into the mass, and subsequently boiling in vacuum.

6. The improvement in the art of disintegrating fibrous, substances, which consists in boiling them in a digester under pressure, draining off the liquor, whereby the soluble impurities are removed, then injecting steam into the mass, boiling under vacuum, and drawing off the vapors that arise in the digester, whereby the vaporized impurities are carried off. 7

7. The improvement in the art of disintegrating fibrous substances, which consists in boiling them in a digester under pressure and draining off the liquor,- the-u boiling under vacuum and draining off the liquor, and finally adding fresh water.

8. The improvement in the art of disintegrating fibrous substances, which consists in boiling them in a digesternnder pressure with forced circulation of the liquor through the mass, then drawing off the vapors in the digester while injecting steam to maintain a pressure, then draining off the liquor, and subsequently boiling under vacuum and drawing off the vapors.

9. The improvement in the art of disintegrating fibrous substances, which consists in boiling them in a digester under pressure,then draining off the liquor, boiling again under vacuum, injecting steam, and drawing off the vapors, then draining off the liquor, then introducing water and boiling under pressure, and subsequently boiling again under vacuum.

10. The improvement in the art of disintegrating fibrous substances, which consists in boiling them in a digester under pressure and then under vacuum and finally raising the pressure and blowing out the fibrous matter and liquid into a vacuum-chamber.

11. The improvement in the art of disintegrating fibrous substances, which consists in boiling them in a digester under pressure and then under vacuum, draining off the liquor, introducing fresh liquor, and discharging from the digester, passing the fibrous matter and liquid through a grit-separator, and finally drawing them through a pump.

12. The improvement in the art of disintegrating fibrous substances, which consists in boiling them in a digesterunder pressure and then under vacuum, draining off the liquor, introducing fresh liquid, raising the pressure and blowing out the fibrous matter and liquid into a vacuum-chamber, adding fresh Water, washing the fibrous matter through a series of traps in a grit-separator, whereby theheavier particles are arrested, and drawing the fibrous matter and liquid through a pump.

13. The improvement in the manufacture of paperpul p, which consists in treating fibrous substances in a digester, removing the soluble impurities by boiling and draining off the liquor, removing the vaporizable impurities by boiling in a vacuum and drawing off the vapors, then discharging the fibrous matter and liquid from the digester, and subsequently removing the heavier foreign matters by precipitation. from the fluid pulp.-

14. The improvement in the art of disintegrating fibrous substances, which consists in boiling them in a digester while circulating steam or liquid through the mass and from time to time injecting steam into the digester through its outlet, whereby the material adjacent to the outlet is treated homogeneously with the remaining material.

15. An apparatus for disintegrating fibers, consisting of a digester, a perforated pipe or pipes entering the same, and steam, water, and chemical pipes connected to said perforated pipe and provided with valves, combined and adapted to operate substantially as set forth.

16. An apparatus for disintegrating fibers, consisting of a digester, a perforated-pipe or pipes passing through the same, steam pipes connected to both ends of said perforated pipe, a circulating-pump connected to one end of said perforated pipe, and the delivery-pipe from said pump connected to the opposite end of said perforated pipe, with suitable valves for said pipes, combined and adapted to operate substantially as set forth.

17. An apparatus for disintegrating fibers, consisting of a digester, a perforated pipe or pipes passing through the same, steam, water, and chemical pipes connected to said perfo- IIO rated'pipe, a screen in the bottom of said digester, a drainage-pipe leading from beneath said screen and connecting with said pipes, and a circulatingpump connected to said drainage-pipe and to one end of said perfo rated pipes, and its discharge-pipe extending to and connected with the opposite end of said perforated pipe, all combined together and with suitable valves and adapted to operate substantially as set forth.

18. The combination of a digester, a perforated pipe or pipes entering it, steam, water, and. chemical pipes connected to said perforated pipe, a vacuum-pipe leading from the digester, a pump in connection with said pipe, a branch pipe connecting said perforated pipe with said vacuum-pipe, and suitable valves in the respective pipes, arranged to operate substantially as set forth.

19. The combination, with a digester, of two or more perforated pipes extending through it, valved crosspipes connected to them at their opposite ends, and a circulatingpump with its suction connected with one of said cross-pipes and its discharge connected to the other, substantially as set forth, whereby the said pump may draw liquid from the digester through one of said perforated pipes and return it thereto through another.

20. An apparatus for disintegrating fibers, consisting of a digester, a valved vacuum-pipe leading from the upper part thereof, and an exhausting device connected to said pipe and adapted to produce a partial vacuum in said digester, and a steam-pipe entering the bottom of said digester, combined and adapted to operate substantially as set forth.

21. The combination of a digester, a vacuumchamber, a suction-pump, an outlet-passage from the digester to said vacuum-chamber, a valve in said passage, a suction-pipe extend; ing from said vacuum-chamber to said pump,

and a suction -pipe extending from the digester and communicating with said pump, substantially as set forth.

22. The combination of a digester, an outlet passage therefrom, a grit-separator, and a force-pump, whereby the contents discharged from the digester pass through the gritfseparator before being drawn into said pump, substantially as set forth.

23. The combination of a digester,a vacuumchamber, an outlet-passage from the digester entering said chamber, a valve in said passage, a force-pump adapted to draw the liquid from the bottom of said chamber, and a suction-pump adapted to draw the air from the upper part of said chamber and thereby to maintain the vacuum therein, substantially as set forth.

24. The combination of a digester,a Vacuumchamber, a valved outlet-passage from the digesterto said chamber, a suction'pump connected to said chamber and adapted to maintain the vacuum therein, an outlet for liquid from the bottom of said chamber, a grit-separator connected to said outlet, and a forcepump with its suction connected to the outlet of said separator and adapted to draw the liquid therethrough against the suction in the vacuum-chamber, substantially as set forth.

25. A digester constructed with double walls forming a water-jacket between, in combination with a pipe extending from the top to the bottom of said jacket and a pump for causing a circulation in said pipe and jacket, substantially as set forth.

In witness whereof I have hereunto signed my name in the presence of two subscribing witnesses.

HENRY BLAOKMAN. Witnesses:

GEORGE H. FRASER, ARTHUR WILTON. 

